The present invention relates to a technique of performance tuning of the whole storage subsystem having storage subsystems that are not directly connected to host computers.
As a result of the recent spread of Internet and adaptation to development of broadband, an amount of information treated by a computer system increases year by year, and importance of information continues to increase. Accordingly, in a computer system, it is requested more and more strongly that a storage used for accumulating information read and written by a host computer (particularly a storage subsystem connected outside the host computer) should have high reliability, for example, in protection of the stored data, in addition to large capacity and high performance.
A disk array system is one method of satisfying these requests together, in a storage subsystem.
In a disk array system, data is distributed and stored into a plurality of physical storage units arranged in an array, realizing data redundancy. Namely, high capacity is obtained by providing a plurality of physical storage units, high performance by operating the physical storage units in parallel, and high reliability by data redundancy.
Disk array systems are classified into five classes, the level 1 through the level 5, depending on configurations for realizing redundancy (For example, D. A. Patterson, G. Gibson and R. H. Kats, “A Case for Redundant Arrays of Inexpensive Disks” (in Proc. ACM SIGMOD, pp. 109 to 116, June 1988) (hereinafter, referred to as Non-Patent Document 1)). There are disk array systems arranged such that data is simply divided and stored into a plurality of physical storage units, without being given redundancy. Such disk array system is called the level 0. In the following, a set of a plurality of physical storage units realizing a certain level described above is referred to as a parity group. Further, a configuration for realizing redundancy is referred to as the RAID configuration.
Costs of constructing a disk-array system and performance and characteristics of the constructed disk array system depend on the level of the disk array system. Thus, frequently, in constructing a disk array system, a plurality of arrays (i.e., sets of disk unit) of different levels is used mixedly, depending on the intended purpose of the disk array system.
Since performance of a disk array system is increased by operating a plurality of physical storage units in parallel, it is required to perform performance tuning, namely, to efficiently distribute data into a plurality of parity groups depending on details of processing to perform.
Physical storage units constituting a parity group are different in their costs depending on their performance and capacities. Thus, sometimes, parity groups are each constructed by combining physical storage units having performance and capacities different from other parity groups. In the case of such a disk array system in which different parity groups have different physical storage units, performance tuning is still more important.
As a technique of realizing performance tuning of a disk array system, may be mentioned, for example, a technique in which a disk array system monitors frequency of access from a host computer to stored data and locates data having higher access frequency onto a physical storage unit of a higher speed (See, for example, Japanese Patent Laid-Open Publication No. 2000-293317 (hereinafter, referred to as Patent Document 1)).
Further, there exists a technique in which, based on a tendency that processing performed in a computer system and I/O accompanying the processing are performed according to a schedule made by a user and thus show daily, monthly and yearly periodicity, a disk array system accumulates using states of each physical storage unit and reallocates data in consideration of a previously-determined processing schedule (See, for example, Japanese Patent Laid-Open Publication No. 2001-67187 (hereinafter, referred to as Patent Document 2)).
As described above, in a disk array system data is distributed into physical storage units such that the data has been allocated having redundancy. In order that a host computer does not need to be conscious of actual storage locations of data in the physical storage units, logical addresses used for the host computer to access the physical storage units are held separately from actual physical addresses of the physical storage units, and information indicating correspondence between the logical addresses and the physical addresses is held.
Accordingly, in the above-described techniques, when data is reallocated, a disk array system changes the correspondence between logical addresses and physical addresses before the reallocation into the correspondence after the reallocation. As a result, even after the data reallocation, a host computer can use the same logical address to access the physical storage units. Such data migration within physical storage units, which does not affect access from a host computer thereafter, is called host transparent migration.
On the other hand, as a technique of increasing the number of storage units that can be accessed from a host computer, to cope with increasing amount of information, there is a technique of enabling a host-computer to access storage units to which the host computer can not directly input and output owing to, for example, interface mismatching (See, for example, Japanese Patent Laid-Open Publication No. 10-283272 (hereinafter, referred to as Patent Document 3)).
According to the technique disclosed in Patent Document 3, a disk array system to which a host computer can directly input and output sends I/O requests and the like from the host computer to a disk array system to which the host computer can not directly input and output.